The present invention concerns a method and a device for managing access to the transmission medium of a multiservice distributed switching network adapted to switch traffic in synchronous circuit-switched mode and in synchronous or asynchronous packet-switched mode.
Current switching systems use either circuit-switched mode or packet-switched mode.
The problem with having these two modes co-exist results from the fact that, on the one hand, the needs of high data rate communications mean that the circuit-switched mode must use multiple space-switched parallel transmission media or multiple time-switched time slots, which is ill-suited to the transfer of sporadic information and leads to loss of capacity (resources are reserved through the call) and, on the other hand, although high data rates can be serviced in packet-switched mode it is not possible to guarantee transmission of synchronous information without lengthy time-delay.
Also, until now packet-switching in distributed switching systems has used:
either a random access protocol (for example the CSMA/CD-IEEE/802.3, ALOHA, etc protocols), in which case the access time to the transmission medium is relatively short but because of collisions, by which is meant simultaneous access to the medium by different stations of the network, the system becomes unstable as soon as its load reaches a particular limit,
or deterministic access protocols (for example the TDMA, IEEE-802.4, IEEE 802.5, etc. protocols) which feature relatively lengthy access delays even where the amount of traffic is very low.
Existing access protocols cannot offer simultaneously a short access time and optimum use of the transmission medium.